The present invention relates to an electrically conductive fabric and more particularly to an electrically conductive fabric superior in all of back leak preventing property of resin, flexibility, yarn fray preventing property, electrical resistivity, and electromagnetic wave shielding property.
It is known to form a metal coating on a fabric, thereby making the fabric electrically conductive, and use the thus-coated fabric as an electromagnetic wave shielding material or a grounding material.
In such an application, the electrically conductive fabric is also required to be flexible because it is often used in an attached state to a housing of an electronic device.
When the electrically conductive fabric is to be used in such a use, it is in many cases cut into a predetermined small size or into fine strips, so there arises the problem that the constituent yarns of the fabric are frayed.
To prevent such a fray of the constituent yarns of the electrically conductive fabric, a resin such as an acrylic resin is imparted to the fabric.
Moreover, when the electrically conductive fabric is to be applied to such a use as mentioned above, the fabric is often required to exhibit flame retardancy and this requirement is increasing. To meet this requirement, a flame-retardant is added to the electrically conductive fabric.
Further, when the electrically conductive fabric is to be used in an attached state to a housing of an electronic device, a pressure-sensitive adhesive or a hot melt adhesive is often applied to the fabric.
In this case, it is required to prevent back leak of the applied resin so as not to deteriorate the quality of the electrically conductive fabric. To meet this requirement, that is, to prevent back leak of the resin, there are performed such weaving and processing as increase the yarn density of the fabric, thereby minimizing pores between the fibers which constitute the fabric.
It is known that the fabric thus increased in its yarn density and having a metallic coating thereon is improved in shielding property.
Generally, however, if the yarn density of a fabric is increased, the fabric tends to become less flexible. If the fabric is plated, it becomes harder. For example, therefore, if the electrically conductive fabric in question is wound round a urethane foam to afford a foam gasket and the foam gasket is used as a substrate grounding material, it is inferior in point of adhesion to a housing of an electronic device and is not desirable as an electromagnetic wave shielding material.
In an effort to avoid such an inconvenience, ultrafine yarns or finished yarns have heretofore been used to improve the flexibility of the resulting fabric.
A plain weave fabric, which is relatively difficult to fray, is also used for diminishing the fray of yarn.
However, in the case where a fabric is produced using the yarns composed of ultrafine filaments or the finished yarns and is then plated, even if the fabric is flexible before the plating, a multifilament yarn which constitutes the fabric is restrained and becomes like a monofilament, so that the fabric becomes less flexible.
Moreover, by merely increasing the density of a fabric, it is difficult to completely minimizing pores formed at warp-weft intersecting points of the fabric and the remaining fiber-to-fiber pores make it difficult to improve the electromagnetic wave shielding property and electrical conductivity. Also, there remains the problem of back leak of resin when the resin is applied in a post-processing.
Further, using an ultrafine yarn or a finished yarn and increasing the yarn density of a fabric results in an increase of cost and of the material surface area, with consequent increase in the amount of metal used in plating and likelihood of an increase of the plating cost.
It is an object of the present invention to solve the above-mentioned problems of the prior art and provide particularly a fabric capable of preventing the back leak of resin while ensuring flexibility and possessing high electrical conductivity and electromagnetic wave shielding property.
The present invention resides in an electrically conductive fabric having a metal coating wherein a percent fabric surface occupancy of warp as a constituent of the fabric is 90% to 110% and that of weft as a constituent of the fabric is 40% to 80%.
The present invention, in a preferred embodiment thereof, resides in the above electrically conductive fabric wherein the fabric is a plain weave fabric.
The present invention, in a further preferred embodiment thereof, resides in the above electrically conductive fabric wherein the fibers which constitute the fabric are synthetic filaments.
The present invention, in a still further preferred embodiment thereof, resides in the above electrically conductive fabric wherein the metal coating on the fabric is formed by an electroless plating method.
The present invention, in a still further preferred embodiment thereof, resides in the above electrically conductive fabric wherein the metal of the metal coating is at least one member selected from the group consisting of silver, copper, nickel, tin, and alloys thereof.
The xe2x80x9cpercent fabric surface occupancyxe2x80x9d as referred to herein is represented by:
Percent fabric surface occupancy of warp (%)=warp width (A)/warp pitch (B)xc3x97100 
Percent fabric surface occupancy of weft (%)=warp width (C)/weft pitch (D)xc3x97100 
in a fabric, as shown in FIG. 1. In the electrically conductive fabric of the present invention, the percent fabric surface occupancy of warp is 90% to 110% and that of weft is 40% to 80%.
By thus increasing the warp density of the fabric, setting the percent fabric surface occupancy of warp at 90% to 110%, allowing the fabric surface to be covered mainly with warp, further by decreasing the weft density and setting the percent fabric surface occupancy of weft at 40% to 80%, it is possible to minimize pores formed in warp-weft intersecting points. Besides, the degree of freedom of weft increases and hence the fabric becomes more flexible.
If the percent surface occupancy of warp is less than 90%, the pores formed in warp-weft intersecting points become large, and if exceeds 110%, not only weavability is impaired, but also the fabric flexibility is impaired; besides, degree of overlapping between adjacent warps increases, whereby the permeation of a plating solution is obstructed at the time of plating and hence it becomes difficult to plate the interior of the fabric.
If the Percent surface occupancy of weft is less than 40%, the yarn is apt to slip and it becomes difficult to effect processing, while if it exceeds 80%, the fabric becomes less flexible and the voids formed in warp-weft intersecting points become larger in size.
The fabric may be subjected to calendering for setting the percents fabric surface occupancy of the fabric constituting warp and weft at values falling under the above ranges.
By adopting the above-mentioned constitution there can be obtained an electrically conductive fabric which, in comparison with conventional fabrics, is more flexible, exhibits less back leak of resin at the time of resin coating, and possesses high electrical conductivity and electromagnetic wave shielding property.
As examples of fibers employable in the present invention, mention may be made of synthetic fibers such as nylon (e.g., nylon 6 and nylon 66), polyester (e.g., polyethylene terephthalate) and acryl (e.g., acrylonitrile), and natural fibers such as cotton and hemp, with synthetic fibers, especially nylon and polyester, being preferred in point of durability.
The yarn denier used is preferably in the range of 10 to 150 denier, more preferably 30 to 100 denier, and the filament denier is preferably in the range of 0.1 to 10 denier. If the yarn denier is smaller than 10 denier, the resulting fabric may be inferior in strength and platability, and the yarn denier exceeding 150 denier is not desirable because the fabric texture would become hard. The filament denier smaller than 0.1 denier is disadvantageous in point of cost and may result in deteriorated platability. The filament denier exceeding 10 denier is not desirable because it would result in the fabric texture becoming hard. Both a circular section yarn and a modified cross section yarn are employable.
The metal coating may be performed using a method known well in the field concerned, but an electroless plating method is preferred. As the metal for coating there is used at least one of silver, copper, nickel, tin, and an alloys thereof.
An elongation of the electrically conductive fabric is preferably less than 1.5% when a load of 1 kg per cm in test cloth width is imposed on the fabric. If the elongation is more than 1.5%, there arises a problem in point of processability, for example at the time of cutting, and it is impossible to attain a high dimensional accuracy. Further, if the fabric is attached in an elongated state to a housing of an electronic device, there is a fear of deteriorated shielding property.